It is known to provide glazings, in particular vehicle glazings, with extruded profiles around the margin of the glazing. Profiles on vehicle glazings act as weather seals, and improve the appearance of glazings when the glazings are in position in a vehicle body. Profiles may also be used to receive and retain an adhesive bead used in fixing the glazing in position in the vehicle body. The material used for extruded profiles usually comprises a suitable polymer, for example, polyurethane or a thermoplastic elastomer.
The conventional extrusion process for extruding polymer profiles on to glazings, usually involves extruding the polymer material through an extrusion nozzle, incorporated in an extrusion head, whilst the head is driven along a path along which it is desired to extrude the profile. The extrusion head is usually driven by a robot which is programmed to follow the extrusion path.
Unfortunately, there are disadvantages associated with conventional extrusion.
When extruding a profile on a curve, for example around a corner of a glazing, there is a difference in circumference between the inner and outer edge of the profile. As a consequence of this, extruded profiles can exhibit imperfections at corners, a problem which is particularly acute with sharp corners (i.e. a corner having a small radius or width).
The problem of extruding on a curve, especially around sharp corners, has been addressed in U.S. Pat. No. 5,108,526. U.S. Pat. No. 5,108,526 discloses a polymer extrusion die apparatus wherein polymer is supplied to the die head by means of at least one supply line. The supply line(s) delivers polymer under pressure to at least one supply channel, at least one of which includes means for controlling the flow of polymer therethrough. By using the means for controlling the flow of polymer through a supply channel, the flow of polymer through the inner or outer portion of the die orifice can be controlled. On a corner, the supply channel to the outer portion of the die is controlled to have a higher polymer flow than the inner portion resulting in an improved profile being extruded.
However, there is a further problem in extruding profiles on curves, especially extruding around sharp corners. Commercially available robots typically have six axes of motion which may be insufficient to allow precise extrusion around relatively sharp corners. Thus, it may be difficult to extrude a profile which follows the edge of the glazing precisely when the profile is to be extruded around a relatively sharp corner.
U.S. Pat. No. 5,316,829 discloses extruding a profile on a glazing and then after extrusion, and in a separate step, completing the profile with a complementary component. This is accomplished by using a mould that rests on the glazing, connecting the mould to the profile and injecting into the mould a hardenable material which adheres to the polymer. U.S. Pat. No. 5,316,829 further discloses that where a glazing has a pointed corner where it is difficult to extrude a profile, it is possible to stop the extrusion in the corner, or if the profile has already been produced, to remove the profile after hardening, and to complete or repair it by casting the profile part.
This procedure has disadvantages in that moulding corner parts in a separate step complicates manufacturing and is expensive. Furthermore, a moulded corner will either consist of a material different to that of the extruded profile, or will consist of the same material but produced using different process parameters to those used to produce the extruded profile. As a consequence, the corner portion and the extruded portion of the profile may have different material properties including different adhesion properties. For example, they may exhibit different wettability to adhesives and/or to water (e.g. rain water) and may have different ageing properties. Also, the primer used to bond the material to glass may be degraded by the heat generated by the mould, or may consist of a different material and therefore the adhesion value may be different from that of the extruded profile. Such a difference in materials properties and/or adhesion properties results in the profiled glazing being less reliable in use and in the interface between the corner portion and extruded portion being visible as a seam in the profile. A seam in the profile is unattractive and, therefore, undesirable in a commercial product.